This invention relates to a standing-stem timber harvesting system for harvesting topped tree trunks directly from the stump, preferably making use of a helicopter, but conceivably a dirigible, to sever, hoist and remove the harvested log.
For selective harvesting of individual tree trunks, trees are conventionally individually felled and de-branched. Felling trees often causes damage to the felled tree trunk and invariably causes damage to undergrowth. Removal of the felled tree trunks (i.e., logs) is often difficult, particularly in rugged terrain. Helicopters may be used to pick up felled and trimmed logs and to carry them to a stacking area, to a watercourse, or even directly to a logging truck. One system of lifting and transporting felled timber is disclosed in Jarman U.S. Pat. No. 4,152,019 granted on May 1, 1979. The technique described in that patent requires that conventional felling procedures be used, which can damage the log and inevitably cause damage to the immediate area on which the felled tree falls.
Published Russian Patent Application No. RU 2,095,698 discloses a logging method in which the trunk of a standing tree is cut from two sides, leaving a connecting portion between the saw cuts. Wedges are driven into the saw cuts and vertical members of a securing device are mounted around the tree in such a manner that the connecting portion can later be sawed away. The connecting portion is eventually sawn away, leaving the cut tree standing on the stump (secured in place by the securing device). The cut tree can later be lifted clear by means of a helicopter. This method requires the acquisition of a number of securing devices, if a number of trees are prepared at the same time for being harvested before the arrival of the helicopter. Each such securing device has to be stocked, maintained, transported to the site, installed and removed. Such manipulation complicates the process and increases the overall cost of the logging. Further, according to this method, the ground crew must visit the tree twice, once to saw the tree part way through, and then again later to saw through the connecting portion. As terrain is often difficult, requiring the ground crew to visit the tree twice is time-consuming and expensive.
Despite these earlier methods, there remains a need for an improved method for selectively logging relatively large trees which is economical to utilize for many different situations. Helicopter-implemented techniques have been promising, but have heretofore suffered from disadvantages of which the above-described inadequacies are typical.
The invention is in one aspect a method of standing-stem log harvesting that allows a tree trunk to be harvested without felling. To this end, once severed from the stump, the tree trunk is removed directly upwards by means of a helicopter or equivalent airborne vehicle.
According to the method, a selected tree is first topped. Then, a first saw cut is made through the trunk of the tree near ground level. This first cut should extend generally horizontally into the tree trunk more than about half the diameter of the trunk at the point of cutting (i.e., more than about half a diameter generally perpendicular to the line defining the limit of cutting), and no more than about two-thirds of such diameter. Then a second cut through the trunk from the opposite side is made, terminating at a cut edge generally aligned with and generally parallel to the cut edge of the first cut, preferably in the same horizontal plane as the first cut, and separated from it by holding wood.
Note that in contradistinction to the two cuts conventionally made to fell a tree, which are conventionally vertically offset from one another, the two cuts of the method of the invention are in generally the same horizontal plane. Further, the present technique, again in contradistinction to conventional practice, does not require any notching of the tree prior to sawing; indeed, such notching would be counterproductive. By xe2x80x9cholding woodxe2x80x9d is meant a relatively narrow portion of uncut wood extending substantially from one side of the trunk to the other, and sufficiently thick and strong, with auxiliary support, to impede breaking by wind forces, etc. of the topped trunk away from what will become the stump. The auxiliary support conveniently is provided by driving support wedges into both cuts to stabilize the trunk, so that the wedges and the holding wood maintain the trunk stable and upright until it is harvested.
The holding wood is readily frangible in response to generally horizontal pivoting force applied to the trunk near the top in a direction generally perpendicular to the cut edges (and therefore generally perpendicular to the long dimension of the holding wood), thereby to cause the trunk to pivot about the holding wood, and to permit the trunk to be broken away from the stump for removal. The horizontal holding wood breaking force is preferably applied by a grapple supported by and suspended from a helicopter, as described below.
The selection of the thickness of the holding wood will depend upon a number of factors, including the length and diameter of the tree trunk to be harvested, the species of tree, prevailing conditions (especially susceptibility to strong winds), the forces applied by the helicopter rotor wash, and possibly other factors, and is best empirically determined.
When the log is ready to be harvested, a helicopter provided with a suitable grapple suspended underneath the helicopter manoeuvers into position over the tree trunk so that the grapple engages and grips the top of the trunk. Once the grapple grips the top of the trunk, then by moving the helicopter in a direction generally perpendicular to the cut edges (and thus the long dimension) of the holding wood, the helicopter is able to apply sufficient force to the trunk to break the holding wood. (In the process, the helicopter may dislodge some or all of the wedges.) It may be necessary to apply the horizontal pivoting force alternately in both directions perpendicular to the cut edges until the holding wood breaks. A ribbon or other marking may be affixed to the top of the topped tree trunk to indicate (to the helicopter pilot) the direction of the cuts made into the tree trunk, facilitating correct orientation of the helicopter movement required to break off the log from the stump. Once the holding wood is fractured, the helicopter then removes the severed log and carries it suspended in vertical orientation to a selected drop site.
It is conceivable that a dirigible could be substituted for a helicopter, although wind-related problems, slower and less agile maneuverability, and other negative factors associated with the use of a dirigible, would not be easily overcome.
Apparatus according to the invention suitable to implement the foregoing method comprises, in combination, a helicopter and a grapple carried by the helicopter for gripping and carrying the top of a topped standing tree trunk. The grapple in operation accordingly is oriented so that it grips the trunk while the trunk is vertical, in contradistinction to the orientation of grapples used to grip felled trees. The grapple is preferably of the jaws type, having opposed gripping jaws pivotally movable in a generally horizontal plane for engaging the tree trunk top. The grapple is operable from the helicopter for opening and closing thereof, so as to permit the grapple to releasably grip a tree trunk. The grapple is preferably suspended on a wire rope or other suitable load supporting line (sometimes referred to herein as a xe2x80x9csupport cablexe2x80x9d) underneath the center of gravity of the he copter. The load-supporting line should be sufficiently long that the grapple is within the field of vision of the pilot of the helicopter, and may be made longer or shorter as circumstances require. For example, if the forest canopy is relatively shallow, a shorter load-supporting line may be used; if the forest canopy is relatively deep, then a longer line can be used.
To facilitate guiding the grapple into engagement with the topped tree trunk, a guide line may be suspended under the nose of the helicopter and attached to the grapple, so that when the grapple is not bearing the load of the log, the grapple can be positioned generally vertically under the nose, facilitating the pilot""s view of the grapple and facilitating engagement of the grapple with the topped tree trunk. The guide line should be sufficiently strong to support the weight of the grapple so that the grapple may hang more or less vertically under the nose. The use of a guide line also tends to impede spinning of the grapple on the support cable. Note that if the grapple at the end of the load-supporting line under the center of gravity of the helicopter is sufficiently visible to the helicopter pilot, and if the support line is sufficiently stiff so as to resist spinning of the grapple, no guide line is necessary. In such case, the support line is preferably a non-rotating line; such support lines are commercially available. To stabilize the grapple further, a gyroscopic stabilizing mechanism could be attached to the grapple, but this would increase the cost of manufacture of the equipment.
The guide line, if present, may be in part elastically extensible or may be connected by a recoiling device (line-winding drum or the like) to the helicopter so that its length may vary as between guiding mode and log suspension mode. When the grapple is not carrying a log, the grapple under the elastic or recoiling force moves forward underneath the nose of the helicopter for better visibility. Later, while when the grapple is carrying a log, the guide line elastically extends (or pulls out of the recoiling device) so that the grapple and the log it carries are positioned directly underneath the center of gravity of the helicopter, suspended by the support line. Since the guideline and associated apparatus add complexity and expense, a competent helicopter pilot may prefer to work without any guideline.
The apparatus required at ground level to effect the cuts and provide support for the partially severed trunk is largely conventional, including a conventional chainsaw and wedges. To facilitate the making of the two cuts with reasonable precision, a pair of elongate guide bars of width equal to the width of holding wood required can be mounted vertically oriented on opposite sides of the tree trunk. These guide bars are positioned somewhat offset from the ends of a selected diameter of the trunk such that the first saw cut made into the trunk to the limit of one pair of vertical side edges of the two guide bars is about one-half to two-thirds the diameter of the trunk, and the second cut to the limit of the other pair of vertical side edges of the guide bar leaves holding wood between the cuts equal to the width of each of the guide bars. (Note that although it is preferable to make the longer cut first, it can be made second, after sawing the shorter cut, as long as the deeper cut is made against the lean of the tree.) A set of guide bars of varying widths can be used to provide holding wood of correspondingly varying widths. The guide bars may be nailed to the trees and if desired may be removed for re-use after the two cuts have been made in a trunk. The guide bars are preferably made of plastic, aluminum, or some other material softer than the teeth of the chainsaw but providing resistance to cutting by the chainsaw, and are preferably made of cheap material in the event that they are discarded and not re-used.
Normally, the cutting and wedging operation at the base of the tree is completed before the helicopter is used to harvest the topped tree trunk as described above. But apparatus is known that combines sawing and gripping functions, although such apparatus has heretofore been used at ground level, and has not been adapted for airborne use. It is doubtful that such apparatus could be modified for airborne use in such a manner that its use would be both economical and safe, but in some circumstances, such modified helicopter-borne combined sawing and gripping apparatus could conceivably be used to top the tree, saw part way through its base, and then grip the top of the tree and pivot the tree to break the holding wood and to harvest the log. Note that in most situations, such apparatus could not effectively penetrate the forest canopy so as to be visible to the helicopter operator when the saw is to be used at the base of the tree, so if such apparatus could be effectively used, it would probably require auxiliary support from one or more ground crew personnel. Presumably a delimbing device would have to be added to delimb the tree sufficiently to enable the apparatus to reach the base of the tree. Further, the longer the supporting line for the sawing apparatus, the more difficult it becomes to manoeuver the apparatus into the correct position relative to the tree trunk. So this hypothetical technical solution using such modified combined sawing/delimbing/gripping apparatus appears to be unattractive.